Epicyclic gear trains, which are also commonly referred to as planetary or star gear, have particular application where a minimum of space is a factor. Therefore, the dimensions of the carrier for the planet wheels or the star wheels must be carefully considered with respect to the relatively small space within which the various parts of the gear train are housed, without sacrificing their ability to sustain the stress under the torsional forces to which they are subjected during their operation. Epicyclic gear systems require precision for smooth and efficient operation, and unless provision is made to counteract the angular distorting forces, their use becomes limited.
As an example, epicyclic gear trains are used in turbine powered vessels and other vehicles to reduce the high engine speed of the turbines. In such case the sun wheel is connected to the turbine, while the internal gear ring is connected to the propeller shaft, generally through another gear. In these turbines, which include substantially wide gear wheels and consequently relatively long shaft pins, deformation and bending of these shafts often occur, which in turn will cause the pinions to become obliquely loaded while engaging the sun wheel and the internal gear ring, with consequent uneven wear.